Various articles and methods of forming electrical connections are well known including soldering, spring-loaded contact pads, welding or the use of electrically conductive epoxy adhesives. However, there are problems in forming a suitably reliable electrical connection between a wire conductor and a terminal pad which is deposited on a substrate such as metal, steel, ceramic, or a substrate comprising one or more metal, steel or ceramic components or layers that are placed in high temperature environments. Unfortunately, most of these well known articles and methods for attaching a wire have an upper temperature limit beyond which the original physical characteristics become unstable so that the electrical connections so formed are incapable of reliably maintaining their attachment integrity over a wide temperature range.
For example, specialized solder is effective up to 280 degrees Celsius at which point the solder will melt and allow the wire to disconnect from the pad. In addition, the application and processing of specialized solder is time consuming. Silver epoxy is also used but silver-loaded epoxy is effective up to 250 degrees Celsius and is expensive and time consuming to process. The use of glass-loaded epoxy extends the temperature range up to 400 degrees Celsius but is also very expensive, time consuming and may contain lead or lead-based alloys. In extremely high temperature environments, spring loaded contacts mounted directly on the arcuate surface have been employed but they are very complicated, time consuming and have a limited operating life. In addition, the integrity of the spring contact reduces with age due to thermal cycling and accelerated oxidation. The integrity of a contact pad will deteriorate fast due to contact bouncing phenomenon and the soft material utilized with a pad.
Other more conventional methods of attachment such as an electric arc or flame-burner welding, narrow gap welding, plasma gap welding, plasma/laser welding, have also been employed, but these are not easily adaptable for film terminal pads on a glass loaded ceramic substrate, a ceramic-based substrate, or a coated substrate.
U.S. Pat. No. 6,039,238, issued to Panaghe, discloses a method of attaching a conductor to a thick film trace by applying pressure to a terminal lug that is affixed to the conductor and ultrasonically welding the terminal lug to the film trace. However, this method is problematic and does not address every installation scenario. For example, a means for applying this method to an arcuate (e.g., cylindrical) substrate is not addressed or contemplated. Furthermore, this method also requires the attachment of a terminal lug to the proximal end of the conductor/wire which can be expensive and problematic. Yet another shortcoming of this device is the requirement that the thick film pad be substantially the same thickness as the terminal lug. This would require either the use of a terminal lug that is very thin or a thick film pad that is very thick.
U.S. Pat. No. 5,422,457, issued to Tang et al., discloses a soldering iron with a separable plug and socket connector so that the heater can be exchanged without an accidental disconnection of the soldering assembly. However, since the temperature at the socket connector is relatively low, it does not address the issue of an electrical connection in a high temperature environment.
U.S. Pat. No. 5,352,109, issued to Benenati, discloses an injection molding apparatus that has an injection nozzle with cartridge heaters in grooves that extend axially along the outside of the nozzle. The heaters are retained in grooves by spring “C” clips. A drawback to this system is that it requires the use of liquid-filled channels or highly conductive metal rods to equalize the temperature of the nozzle from one extremity to another.
U.S. Pat. No. 6,325,615, issued to Johnson et al., discloses a wire electrical connector assembly for removably connecting two wire ends to facilitate replacement of a nozzle heater in a mold. The interconnect is located away from the heater so that it is not subject to high temperature environment. This reference does address the problem of being able to rectify a wiring failure without replacing the entire heater as well as the wiring problems that occur in the connection between the wiring and the nozzle heater in a high temperature environment.
U.S. Pat. No. 6,410,894, issued to Hoffmann et al., discloses an electric heater with a tubular substrate. There is a thick film resistive heating element that is disposed about the tubular substrate and there is a metallic overcoat that encases at least a termination portion of the heating element between the substrate and the metallic overcoat. This reference does not address the issue of removing defective wiring that is directly attached to a nozzle heater in a high temperature environment and is only marginally relevant in that it discloses axially aligned wiring.
U.S. Pat. No. 6,433,319, issued to Bullock et al., discloses a clamping mechanism for attaching a stranded conductor to a conductive coating on a substrate. It does not address the wiring problems that occur in the connection between the wiring and the arcuate substrate in a high temperature environment.
Finally, U.S. Pat. No. 6,530,776, issued to Pilavdzic et al., discloses a current method of attaching a conductor to a thick/thin film pad for a heater that is in thermal communication with an injection nozzle. There are a number of densified electrical connectors connected to a film pad with ultrasonic welding. This reference highlights the problems by showing the amount of work involved to attach the conductors to a thick pad and how difficult it would be to remove them or sever this connection without providing a suggestion regarding what to do if the heater or power supply wire fails other than the replacement of the entire heater.
Therefore, the prior art does not provide a satisfactory connector in a high temperature environment that can be readily separated from the power supply when the heater fails in order to reduce overall machine downtime and therefore, increase efficiency and uptime of the molding system. Having to physically handle the arcuate substrate can damage both the device, e.g., heater, as well as the associated wiring connected to the arcuate substrate. In the prior state of technology, the nature of the pad and the associated methods of attachment make it impossible to re-work arcuate substrate connections by any specific means. Also, it can be very time consuming to disconnect the wiring from the arcuate substrate and reconnect wiring to another arcuate substrate. This can result in significant efficiency loss and associated down time.
There is a need for a reliable connector that can facilitate replacement of the heater or power wiring to provide easy electrical attachment and disengagement of the power supply wires in a high temperature environment. The present invention is directed to overcoming one or more of the problems set forth above.